One of the most photographed buildings in a city known for its Modernista architecture is an abandoned squat.

Some believe this abandoned Brutalist masterpiece inspired George Lucas's Sandcrawler.

The ancient heart of Tunis is an enormous maze of narrow streets and alleyways.

This grand hydraulic installation has provided water for townspeople since the Middle Ages.

Founded in 670, this ancient mosque is an architectural time portal.

The largest salt lake in the Sahara is mysteriously alluring.

An ancient Phoenician citadel once stood at the site where Queen Dido first landed, according to legend.

This gorgeous reading room houses the oldest and largest art history library in the Netherlands.

The largest madrasa in Morocco once housed more than 900 students within its exquisite walls.

The oldest monument in Marrakesh and the city's only surviving example of Almoravid architecture.

Fortune tellers, snake charmers, poets, and storytellers all gather on this historic square in Morocco.

This vast masterpiece of Moroccan architecture spreads across 20 acres.

Deliberately hidden for centuries, the magnificent Saadian Tombs were eventually uncovered in 1917.

The iconic boulevard is the perfect place to catch sight of a bicycling skeleton, a levitating Satan, or a chef with his head stuck in a pizza.

The 2,000-year-old Roman columns are hidden within Barcelona's Gothic Quarter.

Barça football fans might see the insignia hidden in a church window as a divine sign.

A temple to modernity, tucked away amid Barcelona's more well known museums.

A once-secret library of Freemason history in Catalonia.

Barcelona's historic 19th-century sewers, whose foundations were laid in medieval times, are open to the public for exploring.

The largest Art Nouveau complex in the world is a Barcelona hospital with a 600-year-long history.

A once grand hotel now sits eerily abandoned in the Catalan countryside outside Barcelona.

The former 1920s mansion of a prominent Catalan developer was used as the Soviet Embassy during the Spanish Civil War, and there is still a bunker below the garden.

Occupied for six centuries by Franciscan Order nuns, this monastery is an amazing ode to Catalán Gothic architecture.

The water-powered carriages are long gone, but for over a century this funicular railway has been the fastest route to the highest point in Paris.